This invention relates to the field of electronically operated oculometer systems--systems which sense the position and movement of the visual organ or eyeball in a living vertebraed test subject, and more specifically, to apparatus usable as a signal source for stimulating or actuating such oculometer systems.
In many military, medical and machinery control environments, the use of eye movement can be a useful source of command signals for directing the operation of a controlled apparatus. In modern control systems, such ocular responsive arrangements are, in fact, rapidly becoming a technology of choice. In the military environment, for example, the sensing of eye movement of a pilot or an armored vehicle crewmember to accomplish weapon guidance, vehicular steering and other command functions is a currently evolving technology. In other uses of this technology in the medical apparatus field, there is a need for reliable eye movement sensing apparatus to enable severely handicapped patients to communicate with other persons or with life support or living assistance apparatus. Eye movement sensing has also become a useful tool for psychologists and others who study human perception--in the evaluation of reading skills or reading disorders or in the evaluation of TV commercial effectiveness, for example. The use of eye movement sensing for the control of computer or industrial equipment is also now within the realm of technical feasibility.
Although several algorithms for sensing the position and movement of an eye have been proposed, one of the more reliable and technically attractive arrangements for such sensing in at least the case of a human subject is found to reside in the use of selected spectrum energy reflection from the eye. Illumination for this reflection is usually accomplished with a spectral frequency beyond the range of visual response by the eye, and is accompanied by sensing of both the energy reflected from the eye retina and the energy reflected from the eye cornea portion; preferably these two reflections are regarded as being two different signals having a degree of independence.
According to this signal originating arrangement, the infrared reflection from a retina can be expected to appear as a substantially circular optical image while the corneal reflection can be expected to appear also as a somewhat circular optical image residing somewhere within the bounds of the retina reflection image. Such eyeball position sensing systems must, however, be arranged to accommodate a number of real world imperfections or noise source signals, signals which may originate, for example, with the presence of tear fluid in the eye, imperfections or irregularities in the eye components--imperfections such as retina holes or cornea spots, as well as with eyelid closings and dust particles. Oculometer imperfections, such as electronic noise also influence the operation of these sensing systems.
For testing the operation of an oculometer system or the apparatus controlled by an oculometer system, it is often desirable to have a precisely repeatable nonliving organism source of oculometer stimulating signals, signals which can be tailored to resemble a selected input function or to test the limits of the oculometer capability for example. Although signals of this general type could be provided by a human operator by performing a clearly defined routine in a repetitive manner such a human based signal arrangement can be, at once, expensive, unpleasant for the human operator and usually lacking in desired signal precision. Stimulation signals may also be provided by a mechanical apparatus which is arranged to simulate the relevant eye portions and their movement, however, such arrangements are often found to be lacking in desirable flexibility and accuracy. The present invention, therefore, provides a signal sourcing apparatus and method that is capable of overcoming the undesirable features of the heretofore employed signal for an oculometer system.
Oculometer systems per se are known in the patent art; two such systems are described in the patents of Ishikawa, U.S. Pat. No. 3,598,107, and Graf, U.S. Pat. No. 4,109,145. In addition, a device having some of the characteristics of an oculometer but operating on a different principal wherein the movements of a human eye element along multiple intersecting planes are sensed is described in the patent of Abey et al U.S. Pat. No. 3,375,375. An eyesight examination apparatus involving some elements of an oculometer system is also shown in the patent of Siarkiewicz et al. U.S. Pat. No. 4,304,242.